Open circuit voltage increase by substituted spacer and thieno[3,4-c]pyrrole-4,6-dione for polymer solar cells

We reported on two donor polymers containing thieno[3,4-c]pyrrole-4,6-dione(TPD) derivatives as electron withdrawing units for organic photovoltaics (OPVs). To control molecular weight and solubility of polymers, hexyl side chains are inserted to thiophene spacers. Due to the electron donating characteristic of hexyl side chains, highest occupied molecular orbital (HOMO) energy level of polymer is decreased as 0.18 eV, whereas the open circuit voltage is increased to 1.08 V. When bulk heterojunction devices were fabricated, the best PCE value of 0.360% (V_OC = 0.89 V, J_SC = 1.2 mA/cm², FF = 36.3%) under 100 mW/cm² irradiation.     

Low-cost dyes based on methylthiophene for high-performance dye-sensitized solar cells

Three donor–acceptor, π-conjugated (D–π–A) dyes containing methylthiophene or vinylene methylthiophene as π-conjugated spacer were utilised in dye-sensitized nanocrystalline TiO₂ solar cells. The relationship between the structure of the dyes and their photophysical, electrochemical and photovoltaic properties was investigated systematically. The vinyl unit, introduced as the π-conjugated spacer, leads to unfavorable back-electron transfer and decrease of the open-circuit voltage. A dye-sensitized solar cell based on 2-cyano-3-(5-(4-(diphenylamino)phenyl)-4-methylthiophenyl-2-yl) acrylic acid displayed the most efficient solar-to-electricity conversion efficiency of the dyes with a maximum η value of 8.27% (V_oc = 0.72 V, J_sc = 15.76 mA cm⁻², FF = 0.73) under simulated AM 1.5 G solar irradiation (100 mW cm⁻²).     

Nanowires embedded porous TiO2@C nanocomposite anodes for enhanced stable lithium and sodium ion battery performance

A porous carbon nanocomposite with embedded TiO₂ nanowires (NWs) was synthesized using a two-step synthetic method in which carbon matrix was obtained by carbonizing a vacuum dried gel. This unique structure in which TiO₂ nanowires uniformly distributed in and tightly bonded to the carbon matrix shortened the electron transport path and reduced the transmission resistance. Nanoporous structure ensured continuous transfer of Li⁺/Na⁺ and supplied a large specific surface area of 280.82 m² g⁻¹ to provide more active sites. Different from other existing works on TiO₂@C anode materials with TiO₂ loading higher than 60 wt%, the obtained very small amount of TiO₂ (~12 wt%) improved the electrochemical and long-cycle performance of carbon substrate with TiO₂ NWs embedded significantly, due to uniformly distributed TiO₂ NWs throughout the carbon matrix. These TiO₂@C composite anodes could deliver a specific capacity of 286 mA h g⁻¹ at 0.3 C, 197 mA h g⁻¹ at 0.15 C for lithium and sodium ion batteries, respectively. It maintained remarkably stable reversible capacities of 128 and 125 mA h g⁻¹ for lithium and sodium ion batteries at 3 C during 2500 cycles, respectively. Smaller fluctuations and smoother curves demonstrated that sodium ion storage was more stable than lithium ion storage for the TiO₂@C composite anode. In addition, the capacitive contributions of TiO₂@C in both systems are quantified by kinetics analysis.     

Polymer solar cells fabricated with 4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene and alkyl-substituted thiophene-3-carboxylate-containing conjugated polymers: Effect of alkyl side-chain in thiophene-3-carboxylate monomer on the device performance

Four alkyl-substituted thiophene-3-carboxylate containing donor–acceptor (D–A) copolymers were designed, synthesized, and characterized. Thiophene-3-carboxylate was used as a weak electron acceptor unit in the copolymers to provide a deeper highest occupied molecular orbital (HOMO) level for obtaining a higher open-circuit voltage in polymer solar cells (PSCs). The resulting bulk heterojunction PSCs, made of the copolymers and [6,6]-phenyl-C71-butyric acid methyl ester (PC₇₁BM), exhibited different short circuit currents (J_SCs) and open-circuit voltages (V_OCs), depending on the length of alkyl side-chain in the thiophene-3-carboxylate unit. Among all fabricated photovoltaic (PV) devices, PC2:PC₇₁BM (1:1 wt. ratio) showed the highest efficiency with the highest J_SC of 10.5 mA/cm². Although PC5:PC₇₁BM (1:1) displayed the highest V_OC of 0.93 V, the device efficiency was observed to be poor, which is due to poor nanophase segregation. This comparison shows that the side-chain of thiophene carboxylate in these copolymers plays a very important role in the device efficiency.     

Fabrication of efficient nanostructured Co3O4-Graphene bifunctional catalysts: Oxygen evolution,hydrogen evolution,and H2O2 sensing

Nanostructured Co₃O₄-graphene hybrid catalysts are fabricated by a one-step vacuum kinetic spray technique from microparticles of Co₃O₄ and graphite powders. The Co₃O₄-graphene hybrid catalysts with various Co₃O₄ contents are studied concerning the oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in 1.0 M KOH, as well as, H₂O₂ sensing in 0.1 M NaOH. We find that increasing graphene content in the hybrid catalysts results in an overall improvement of the OER electrocatalytic activity due to the enhancement in the charge transfer kinetics. The hybrid catalyst with 25 wt% Co₃O₄ reveals the optimum electrocatalytic activity toward the OER with the lowest overpotential (η) of 283 mV@ 10 mA cm⁻² and superior reaction kinetics with a low Tafel slope of 25 mV dec⁻¹. Besides, the OER stability at 50 mA cm⁻² for 50 h in 1.0 M KOH was verified. The hybrid catalyst with 50 wt% Co₃O₄ revealed the highest activity toward the HER with η of 108 mV@ 10 mA cm⁻², Tafel slope of 90 mV.dec⁻¹, and stability at 50 mA cm⁻² for nearly 30 h. Moreover, it reveals ultrahigh H₂O₂ amperometric detection with superior sensitivity of 18,110 μA mM⁻¹ cm⁻², linear detection range from 20 μM to 1 mM, and a limit of detection of 0.14 μM.     

Electrochemical performance of Li4Ti5O12 anode materials synthesized using a spray-drying method

In this study, spinel lithium titanate (Li₄Ti₅O₁₂, LTO) anode materials were synthesized from two titanium sources (P25 TiO₂, 100% anatase TiO₂) using a spray-drying method and subsequent calcination at various temperatures. The electrochemical performance of both a Li/LTO half cell and a LiNi_0.5Mn_1.5O₄/LTO (LNMO/LTO) full cell were investigated. The electrochemical performance of the LTO material prepared from P25 TiO₂ was superior to that of the LTO prepared from 100% anatase TiO₂. After modification of LTO material with AlPO₄, the LTO coated with 2 wt% of AlPO₄ (denoted “2%AlPO₄-LTO”) provided the best performances. The specific (delithiation) capacities of the 2%AlPO₄-LTO anode material was 189.7 mA h g⁻¹ at 0.1C/0.1C, 184.5 mA h g⁻¹ at 1C/1C, 178.8 mA h g⁻¹ at 5C/5C, and 173.1 mA h g⁻¹ at 10C/10C. From long-term cycling stability tests, the specific capacity at the first cycle and the capacity retention after cycling were 185.5 mA h g⁻¹ and 98.06%, respectively, after 200 cycles at 1C/1C and 182.1 mA h g⁻¹ and 99.18%, respectively, after 100 cycles at 1C/10C. For the LNMO/2%AlPO₄-LTO full cell, the average specific capacity (delithiation) and coulombic efficiency after the first five cycles were 164.8 mA h g⁻¹ and 93.30%, respectively, at 0.1C/0.1C. The specific capacities at higher C-rates were 156.1 mA h g⁻¹ at 0.2C/0.2C, 135.7 mA h g⁻¹ at 1C/1C, 97.5 mA h g⁻¹ at 3C/3C, and 46.5 mA h g⁻¹ at 5C/5C. After twenty-five cycles, the C-rate returned to 1C/1C and the specific capacity, coulombic efficiency, and capacity retention were maintained at 134.1 mA h g⁻¹, 99.17%, and 98.82%, respectively.     

Micro-mesoporous TiO2/SiO2 nanocomposites: Sol-gel synthesis,characterization, and enhanced photodegradation of quinoline

Micro-mesoporous TiO₂/SiO₂ nanocomposite powders have been successfully synthesized by the sol-gel process with different TiO₂/SiO₂ molar ratios and were applied in the UV-photodegradation of quinoline (λ = 254 nm). The structural, morphological, and textural characterization of the powders showed a homogeneous distribution of TiO2 nanoparticles within a porous amorphous SiO2 matrix. Due to the micro-mesoporous character of the materials, their textural characteristics were evaluated by the N2 adsorption method, by comparing BET, DR, Langmuir, and DFT theories. Si₆₀Ti₄₀ powders (60%SiO₂/40%TiO₂) presented the highest specific surface area (SSA) obtained from BET (SSA = 363 m²g^-1), DR (SSA = 482 m²g^-1), and Langmuir (SSA = 492 m²g^-1) due to the adequate particle size of TiO₂ and its high dispersion in the porous matrix. A higher degradation of quinoline in the presence of H₂O₂ (66%) was achieved using Si₈₀Ti₂₀ powders (80%SiO₂/20%TiO₂), as compared to pure sol-gel TiO₂ powders, (51%) under the same reaction conditions (1 UVC lamp - 250W, t = 180 min). The better performance of the Si₈₀Ti₂₀ nanocomposite could be attributed to the small TiO₂ anatase crystallite size (<5.7 nm), high dispersion of these crystallites in the SiO₂ matrix, great specific surface area (DR SSA = 342 m² g^?1), and the formation of Ti–O–Si bond, which is associated with new catalytic sites in TiO₂/SiO₂ composite.     

Smooth and highly-crystalline Ag-doped CIGS films sputtered from quaternary ceramic targets

Sputtering with copper indium gallium selenide (CIGS) ceramic targets could produce smooth CIGS thin films that are preferred for preparing two-terminal tandem devices. However, grain sizes prepared in this way are small and device efficiency was low. To increase the grain size, in this report, an Ag layer was pre-sputtered beneath CIGS. The Ag doping layer increased the grain size and improved the crystalline alignment. Consequently, the Ag-doped films exhibited improved charge mobility. From X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy characterizations, we obtained an optimized Ag thickness of 15 nm. Short-circuit current density (J_SC), open-circuit voltage (V_OC), and fill factor (FF) were all improved after doping with 15-nm Ag. Increasing the annealing temperature from 550 °C to 575 °C, the grains was enlarged further, with the power conversion efficiency (PCE) increasing to 14.33% and V_OC to 545 mV. Upon the smooth CIGS film, a thin conformal perovskite layer was fabricated without polishing. This work demonstrates a simple way to fabricate smooth and highly-crystalline CIGS films that can be used for tandem solar cells.     

Surface modification of electron transport layers based on TiO2 nanorod boosts efficiency of perovskite solar cells

In this work, TiO₂ heterostructure thin films including rutile TiO₂ nanorods (TNRs) and anatase TiO₂ nanoparticles (TNPs) on fluorine-doped tin oxide (FTO) glass are fabricated by the hydrothermal method and are applied as electron transport layers (ETLs) in MAPbI₃-based perovskite solar cells (PSCs). To enhance the surface area of ETL, TNRs are first etched in acidic solution by another hydrothermal process for different reaction times before coating with TNPs. The morphological and structural properties of TNRs after etching are carefully investigated. Interestingly, the surface modification of TNR thin film by appropriate TNP deposition and etching improves significantly the efficiency of PSC devices by more than 1.6 times. To further improve the performance of PSC, phenyl-C61-butyric acid methyl ester (PCBM) is used to enhance the charge transfer efficiency at the ETL/perovskite interface, and the optimal PSC device shows the champion efficiency of 18.50% with low charge transfer resistance (11.56 ohms).     

Significantly improved photoluminescence of the green-emitting β-sialon:Eu2+ phosphor via surface coating of TiO2

The β-sialon:Eu²⁺ phosphor particles were successfully coated by TiO₂ nanoparticles via the sol-gel method. The TiO₂-coated β-sialon:Eu²⁺ phosphor had a significantly improved photoluminescence (PL) performance under the 365 nm excitation, due to the localized surface plasmon resonance (LSPR) at the interface between the TiO₂ coating layer and phosphor surface. The emission intensity of the TiO₂-coated β-sialon:Eu²⁺ prepared with the titanium (IV) tetrabutoxide (Ti(OC₄H₉)₄, TTBO):H₂O = 1:0.5 volume ratio was dramatically increased by ~24%. When the preparation temperature was 500°C, it was responsible for superior PL intensity by considering the important domination factors of higher anatase content and spherical particle shape of the TiO₂ coating layer to the LSPR effect. The coating around the phosphor surface by the TiO₂ nanoparticles would be an effective technique to improve the PL efficiency of phosphor for the application in the white light-emitting diodes (LEDs), by utilizing the LSPR effect of the semiconductor coating layer, instead of conventional metal plasmonic materials.     

Synthesis, characterization, and photovoltaic property of a low band gap polymer alternating dithienopyrrole and thienopyrroledione units

The lower the highest occupied molecular orbital (HOMO) energy level of the conjugated polymer is, the higher the open-circuit voltage (V_OC) of the obtained polymer solar cell (PSC) is. To achieve this goal, a new conjugated polymer (PDTPTPD) alternating dithienopyrrole (DTP) and thienopyrroledione (TPD) units was designed and synthesized by Stille coupling reaction. Through UV-vis absorption and cyclic voltammetry (CV) measurements, it was found that the resulting copolymer exhibited both a low optical band gap of 1.62 eV and a low HOMO energy level of −5.09 eV owing to the electronegativity of TPD moiety. Preliminary photovoltaic study disclosed that the PSC based on PDTPTPD:PCBM ([6,6]-phenyl-C₆₁ butyric acid methyl ester) blend showed a power conversion efficiency (PCE) of 1.9%, with a V_OC of 0.70 V, and a short circuit current (I_SC) of 6.97 mA/cm², suggesting that PDTPTPD is a promising photovoltaic polymer.     

Novel D-π-A system based on zinc porphyrin dyes for dye-sensitized solar cells: Synthesis, electrochemical, and photovoltaic properties

We have designed and synthesized novel zinc porphyrin dyes which have a D-π-A system based on porphyrin derivatives containing a triphenylamine (TPA) electron-donating group and a phenyl carboxyl anchoring group substituted at the meso position of the porphyrin ring, yielding the push-pull porphyrins as the most efficient green dye for dye-sensitized solar cell (DSSC) applications. The synthesis and characterization of a novel D-π-A system based on zinc-porphyrin derivatives have been investigated through their photophysical and photoelectrochemical studies. A large red-shift of the absorption maxima due to introduction of the TPA moiety at the meso position of the porphyrin ring was expected in the D-π-A porphyrins, but the absorption maxima of HKK-Por dyes were a little red-shifted in contrast to Zn[5,-10,15-triphenyl-20-(4-carboxylphenyl)-porphyrin], due to the tilted structure between TPA and the porphyrin unit. Under the photovoltaic performance measurement, the maximum incident photon-to-current conversion efficiency (IPCE) value of the DSSC based on HKK-Por 5 was slightly higher than the efficiencies of the DSSCs based on other HKK-Por dyes due to the introduction of the alkoxy group into the TPA moiety at the meso position of the porphyrin ring. A maximum photon-to-electron conversion efficiency of 3.36% was achieved with the DSSC based on HKK-Por 5 dye (J_SC = 9.04 mA/cm², V_OC = 0.57 V, FF = 0.66) under AM1.5 irradiation (100 m Wcm⁻²).     

Bulky side-chain density effect on the photophysical, electrochemical and photovoltaic properties of polythiophene derivatives

Low band-gap polythiophene (PT) derivatives, with bulky conjugated side-chains composed of the triphenylamine, thiophene, and vinylene groups (TPATh), are synthesized. The copolymers, synthesized by Grignard metathesis and Stille coupling with different copolymer configurations and side-chain densities, are regioregular-TPATh-PT (rr-TPATh-PT) and random-TPATh-PT (r-TPATh-PT), respectively. The incorporation of bulky conjugated moiety curtails the effective conjugation length in the main chain; thus, low HOMO levels are obtained for the copolymers. Moreover, r-TPATh-PT with less bulky side-chain content exhibits a better conjugation along the polymer backbone than rr-TPATh-PT. Higher absorption intensity in the vision region is observed for r-TPATh-PT in comparison with rr-TPATh-PT. In addition, polymer solar cells (PSCs) are fabricated based on an interpenetrating network of PT derivatives as the electron donor and the fullerene derivatives (PC₆₁BM and PC₇₁BM) as the electron acceptors. Better compatibility is observed for the r-TPATh-PT/PC₆₁BM-blend film as compared to the rr-TPATh-PT/PC₆₁BM-blend film. Higher photovoltaic (PV) performances of the r-TPATh-PT/PC₆₁BM-based PSCs are observed in comparison with the rr-TPATh-PT/PC₆₁BM-based PSCs. The power conversion efficiency (PCE) of the PSC based on the blend of r-TPATh-PT and PC₆₁BM (w/w = 1:1) reaches 0.94% under an illumination of AM 1.5G, 100 mW cm⁻², which is almost twice that of the cell based on rr-TPATh-PT. Further improvement of PV performance is achieved for the PSC fabricated from the blend of r-TPATh-PT and fullerene derivative PC₇₁BM (w/w = 1:3), with a short-circuit current of 6.83 mA cm⁻², an open-circuit voltage of 0.71 V and a PCE of 1.75%.     

Lead free CsSn0.5Ge0.5I3 perovskite solar cell with different layer properties via SCAPS-1D simulation

Organic–inorganic halide perovskite solar cells (PSCs) have been extensively studied due to their simple fabrication methods and obvious device efficiency advantages. In this work, the perovskite CsSn_0.5Ge_0.5I₃ is used as the light absorption layer, which is doped with Ge²⁺ in CsSnI₃ to improve its stability. The polymers of 3-hexylthiophene (P3HT) with excellent optoelectronic properties and low price, and SnO₂ with high electron extraction ability is selected as charge transport layers. Based on these, a novel PSC structure (FTO/SnO₂/IDL1/CsSn_0.5Ge_0.5I₃/IDL2/P3HT/Au) has been simulated via solar cell capacitor simulator (SCAPS-1D). The PSC performance is optimized by adjusting a series of parameters, including the layer thickness, defect density, electron affinity potential energy, and operating temperature, and so forth. The results show that the PSC defects are passivated by adjusting the appropriate parameters, and the final optimized open circuit voltage (V_OC) is 1.08 V, short-circuit current density (J_SC) is 27.37 mA/cm², fill factor (FF) is 83.32%, while the power conversion efficiency (PCE) is increased from the initial 10.89% to 24.63%, which provides theoretical reference for experiments and new ideas for the preparation and development of efficient and environmentally friendly PSCs. Finally, the effect of different metal cathodes with and without hole transport layer (HTL) on PSC performance is compared. The PSCs without HTL are more dependent on battery cathodes, which provided a way to replace precious metals with other electrode materials.     

Stable composite electrolytes of PVDF modified by inorganic particles for solid-state lithium batteries

Polymer electrolytes have been attracting much attention because of their flexibility and easy follow-up processing, but their Li⁺ conductivity in lithium-metal batteries (LIBs) is unsatisfactory. Stable composite electrolytes of poly (vinylidene fluoride) (PVDF) polymer with high lithium-ion conductivity have been prepared by a trigger structural modification of Li_6.5La₃Zr_1.5Nb_0.25Ta_0.25O₁₂ (LLZNTO) garnet ceramic and TiO₂ oxide. The influences of various amounts of TiO₂ and LLZNTO on electrochemical performance were systematically examined. These composite electrolytes exhibited maximal Li⁺ conductivity of 2.89 × 10⁻⁴ S cm⁻¹, which is consistent with the value of pure ceramic electrolytes. Furthermore, it possessed the stable long-term Li cycling and the wide electrochemical window, involving repeated Li plating/stripping at 0.2 mA cm⁻² over 280 h without failure. The discharge specific capacity and Coulomb efficiency for all-solid-state LIBs assembled with these membranes delivered outstanding cycling stability with high discharge capacities (117.9 mA h g⁻¹) at 0.1 C rate and Coulomb efficiency reached 99.9% after 25 cycles. The high Li⁺ conduction capability can be ascribed function of introducing TiO₂ and LLZNTO to restrain tremendously the crystalline behavior of the polymer. Furthermore, the LLZNTO can be complex with PVDF for dehydrofluorination, and it can also offer a burst transportation route for lithium ions. This system might serve as an attractive use for polymer solid electrolytes and open up new possibilities for safe all-solid-state LIBs.     

Cu2ZnSnS4 as a hole-transport layer in triple-cation perovskite solar cells: Current density versus layer thickness

Cu₂ZnSnS₄ (CZTS) is a good candidate for cost-effective perovskite solar cells (PSCs) due to its direct bandgap with a value of 1.4–1.5 eV. In this study, we investigate CZTS ink as an inorganic hole-transport-layer (HTL) in CsMAFAPbIBr mixed halide PSCs. We study the cell efficiency and hole extraction from the perovskite layer for different thicknesses of HTL. The optimized device exhibits better hole selectivity, and the best efficiency of the device (12.84%) is achieved for the CZTS layer with a thickness of 159 nm. The prepared samples were also tested by open-circuit voltage decay analysis and electrochemical impedance spectroscopies. Results show that the optimized device effectively prohibits the electrons-holes recombination with a charge transfer resistance of 9.38 Ω cm². This work suggests that the optimal thickness of CZTS as an HTL in triple-cation PSC is about 159 nm by giving short-circuit current density of 23.69 mA cm^?2.     

Uniform coating of a crystalline TiO2 film onto steel plates by electrochemical deposition using staged pulse current

A crystalline TiO₂ (c-TiO₂) film was electrochemically deposited onto a 10 cm × 20 cm hot-dip-galvanized (HDG) steel plate at 60 °C from an alkaline aqueous solution containing 0.1 M titanium potassium oxalate dehydrate and 1 M hydroxylamine. The electrochemical deposition was carried out by a galvanostatic method. First, a current density of 10 mA cm⁻² was applied for 5 min, which led to the formation of a uniform coating of TiO₂ on a 1 cm × 1 cm small HDG plate. A crystalline layer was observed, however, only in the central area, whereas the upper and the edge areas were amorphous. Both calculations and experiments confirmed that this was due to the difference of the local current densities in the vicinities of different areas. Next, three different currents (5 mA cm⁻² (2 min), 10 mA cm⁻² (2 min) and 20 mA cm⁻² (1 min)) were applied continuously so that the local current density for each part of the substrate achieved appropriate deposition conditions. The film thus obtained was crystalline in all areas and of uniform thickness.     

Organic dyes incorporating low-band-gap chromophores based on π-extended benzothiadiazole for dye-sensitized solar cells

A series of new π-conjugated organic dyes (HKK-BTZ1, HKK-BTZ2, HKK-BTZ3 and HKK-BTZ4), comprising triphenylamine (TPA) moieties as the electron donor and benzothiadiazole moieties as the electron acceptor/anchoring groups, was synthesized for the use in dye-sensitized solar cells (DSSCs). TPA units are bridged to benzothiadiazole with single(S), double(D) and triple bonds(T) in different derivatives. And HKK-BTZ1 was modified by introducing alkoxy group of TPA unit, because the bulky alkoxy group is a strong donating group for the more red shift and for reducing aggregation of dyes in TiO₂ film. The structure-property relationship was investigated. Under standard global AM 1.5 G illumination, a maximum photo-to-electron conversion efficiency of 7.30% was achieved with the DSSC based on dye HKK-BTZ4 (J_SC = 17.9 mA/cm⁻², V_OC = 0.62 V, FF = 0.66), while the Ru dye N719-sensitized DSSC showed an efficiency of 7.82% with a J_SC of 17.5 mA/cm⁻², a V_OC of 0.62 V, and a FF of 0.72.     

Structural,morphological, and optical studies of hydrothermally synthesized Nb-added TiO2 for DSSC application

Herein, titanium dioxide (TiO₂) nanoparticles doped with various concentrations (0–7 wt %) of niobium (Nb) are hydrothermally synthesized and used effectively as a photoelectrode for application in dye-sensitized solar cells (DSSCs). The rutile-to-anatase phase transition, accompanied by a change in crystallite size from 23.75 to 9.77 nm, is confirmed via X-ray diffraction (XRD) and Fourier transform (FT)-Raman spectroscopy. In addition, the prepared Nb–TiO₂ nanoparticles exhibit a spherical morphology with a mean grain diameter of 43.38–50.69 nm. Further, X-ray photoelectron spectroscopy (XPS) indicates a shift in the Fermi level of the TiO₂ towards the conduction band minimum, and an increase in the bandgap from 2.69 to 2.88 eV, with increasing Nb concentration. The resulting increases in the short-circuit current density (J_SC) and open circuit voltage (V_OC) with the increased injection and conductivity of electrons lead to the enhancement of the DSSC performance. EIS measurements represents the effect of Nb doping on charge transporting and recombination behavior of DSSCs. Moreover, the Nb–TiO₂-based DSSCs provide a better power conversion performance as compared to that of the pristine TiO₂.     

High-performance 0.9Al2O3-0.1TiO2 microwave dielectric ceramics prepared by digital light processing

In this work, the 0.9Al₂O₃-0.1TiO₂ ceramic sample with good microwave dielectric properties and complex structures can be well fabricated by digital light processing (DLP). A relationship between dispersant content and rheological behavior of 0.9Al₂O₃-0.1TiO₂ slurry was explored. When dispersant content was 3.0 wt%, 0.9Al₂O₃-0.1TiO₂ slurry with high solid loading (50 vol%) and low viscosity (2.9 Pa s) could be obtained. 0.9Al₂O₃-0.1TiO₂ ceramic parts with high accuracy were fabricated successfully by adding 3.0 wt% photoinitiator under 600 mJ/cm² exposure energy. With the increase of sintering temperature from 1400 °C to 1600 °C, relative density, dielectric constant (ε_r), and quality factor (Q × f) of 0.9Al₂O₃-0.1TiO₂ ceramic sample increased first and then decreased, and all reached the maximum value at 1550 °C due to the uniformity and densification of microstructures. The temperature coefficient of resonant frequency (τ_f) value showed an almost monotonous increase, changing from negative to positive, and near-zero τ_f value at 1550 °C. In addition, 0.9Al₂O₃-0.1TiO₂ ceramic samples sintered at 1550 °C fabricated by DLP method presented much better microwave dielectric properties: ε_r = 11.30 ± 0.02, Q × f = 35,345 ± 143 GHz (@～12 GHz), τ_f = 2.16 ± 0.21 ppm/°C than that of by dry pressing method: ε_r = 11.16 ± 0.11, Q × f = 30,195 ± 257 GHz (@～12 GHz), τ_f = 4.45 ± 0.13 ppm/°C, especially the Q × f value achieved a 17% increase. Accordingly, DLP technique, which has advantages of producing relatively high properties and complex geometry of microwave dielectric ceramics as well as without extra high-cost mold, greatly satisfies application requirements.